The present invention relates to a cutter driving apparatus to be incorporated into a boring machine.
A boring machine provided with a cutter driving apparatus shown in FIGS. 7(a) and 7(b) is disclosed in the specification of U.S. Pat. No. 6,280,123. In this cutter driving apparatus, a cutter 114 is attached to a spindle 112, which rotates integrally with a drive shaft 106 disposed in a housing 105.
Since the drive shaft 106 and the spindle 112 are connected to each other with a spline 113, the spindle 112 can move relative to the drive shaft 106 along the axis 106a thereof. A quill 115 rotatably surrounds the spindle 112 and is movable integrally with the spindle 112 along the axis 106a. A pinion 118 is meshed with a rack 119 provided on the quill 115 and is rotated by operating an operation handle (not shown). Thus, when the pinion 118 rotates, both the quill 115 and the spindle 112 move along the axis 106a. 
When the spindle 112 moves along the axis 106a, the distance over which a cutter 114 attached to the spindle 112 moves, the stroke S shown in FIG. 7(a), depends upon the length of the rack 119. However, the length of the rack 119 is subject to the design limitation so as to avoid interference of the rack 119 with members located around the drive shaft 106 and spindle 112. Thus, the stroke S is not very long. Therefore, the conventional boring machine is unable to form deep bores.